Insulated electric conductor

ABSTRACT

In order to increase the adhesion of an insulating coating ( 2 ) to an electric conductor ( 1 ), preferably of copper or aluminum, an insulated electric conductor comprising an electric conductor ( 1 ), preferably made of copper or aluminum, with an insulating coating ( 2 ) is proposed according to the invention,
     wherein the insulating coating ( 2 ) either comprises
       at least one insulating layer ( 3 ) made of thermoplastic material,   
       or
       the insulating layer ( 3 ) and a plastic-containing intermediate layer ( 4, 5 ),   
       obtainable by a method in which the electric conductor ( 1 ) is placed under a protective gas atmosphere and is bombarded with ions of the protective gas in a gas plasma in order to remove an oxide layer formed on a surface of the electric conductor ( 1 ) and/or to increase the surface energy of the electric conductor ( 1 ),   and subsequently either
       the at least one insulating layer ( 3 )   
       or, in the case that the coating ( 2 ) comprises the plastic-containing intermediate layer ( 4, 5 ),
       at least the plastic-containing intermediate layer ( 4, 5 ) is applied directly to the surface of the electric conductor ( 1 ) under a protective gas atmosphere.

FIELD OF THE INVENTION

The invention relates to an insulated electric conductor comprising anelectric conductor, preferably of copper or aluminum, having aninsulating coating, wherein the insulating coating comprises at leastone outer insulating layer made of thermoplastic material, and to amethod for producing such an insulated electric conductor.

DESCRIPTION OF THE PRIOR ART

Insulated electric conductors are installed in almost any electricaldevice to conduct electrical current without causing short circuits thatmay be caused by the contact of non-electrically insulated conductors.Such insulated electric conductors comprise a copper electric conductorand a coating electrically insulating the electric conductor, whichusually comprises one or more layers. In order to ensure the insulationof the electric conductor, the insulating coating comprises aninsulating layer of thermoplastic material (also called thermoplasticresin, thermoplastic synthetic material or thermoplastic polymer).

While it is advantageous in many applications that the adhesion of theinsulating coating to the electric conductor is weak to allow easystripping of the electric conductor, it is desirable in otherapplications to ensure the greatest possible adhesion. Such applicationscan be found for example in electrical engineering and in particular inelectric motors or transformers, where the insulated electric conductorsare also exposed to an elevated temperature. The processability of theinsulated electric conductors often requires increased adhesion of theinsulating coating to the electric conductor, in some cases even at highoperating temperatures.

In order to check the adhesion, a round cut is usually carried out onthe insulated electric conductor perpendicular to a conductor axis, theelectric conductor is stretched by 20% and then the detachment of theinsulating coating from the electric conductor is measured. The lowerthe detachment of the insulating coating from the electric conductor,the better the adhesion.

In conventional insulated electric conductors having an insulatingcoating with an insulating layer which is preferably highlytemperature-resistant, the adhesion between the electric conductor, inparticular made of copper, and the insulating coating, in particular theinsulating layer, is rather low, since the adhesion of a plastic to theelectric conductor is low due to the surface properties.

OBJECT OF THE INVENTION

It is therefore an object of the invention to propose an insulatedelectric conductor which overcomes the disadvantages of the prior artand ensures good adhesion between the insulating coating and theelectric conductor.

SUMMARY OF TEE INVENTION

The electric conductor of generic insulated electric conductors consistsof copper or an alloy with a high copper content or aluminum or otherelectrically conductive materials. The electric conductor is understoodto mean both a single conductor and a strand containing severalindividual conductors. The cross-sectional geometry of the electricconductor, which is normal to a conductor axis, can have any geometricshape: square, rectangular, circular or elliptical, wherein it iscustomary to round off any edges, or they are profiled. The insulationof the electric conductor is ensured by the at least one providedinsulating layer of thermoplastic material (also called thermoplasticresin, thermoplastic synthetic material or thermoplastic polymer),wherein the at least one insulating layer can advantageously form theoutermost layer of the insulating coating. However, it is alsoconceivable for one or more additional insulating layers to be appliedto the at least one insulating layer.

By contact with oxygen which is unavoidable if the electric conductor isexposed to the atmosphere, an oxide layer, e.g. copper oxide or aluminumoxide, forms on the surface of the electric conductor. Extensive seriesof experiments have shown that the oxide layer has a negative effect onthe adhesion properties of a layer of the insulating coating applied tothe surface of the electric conductor.

However, when the oxide layer is removed, the adhesion of the layer ofthe insulating coating applied to the surface of the electric conductorremoved from the oxide layer is significantly improved. It has beenshown that the oxide layer can be completely removed by a plasmatreatment under an (oxygen-free) protective gas atmosphere, whereinother impurities can be removed by the plasma treatment. It is evenpossible that the top atomic layers of the electric conductor areremoved by the plasma treatment.

In the plasma treatment, a gas plasma is generated in the protective gasatmosphere and the electric conductor in the plasma is bombarded withions of the protective gas in order to remove at least the oxide layerby the ion bombardment. For example, nitrogen, argon or hydrogen issuitable as a protective gas or process gas. The plasma treatment has inaddition to the removal of the oxide layer further positive effects onthe insulated electric conductor: on the one hand, the electricconductor is heated by the impact energy of the ions on the surface andcan be annealed during the plasma treatment to recrystallize thestructure of the electric conductor; on the other hand, the ionbombardment increases the surface energy of the electric conductor,which additionally improves the adhesion of the insulating coating tothe surface of the electric conductor. In this context, this is alsoreferred to as an activation of the surface of the electric conductor.Another effect of the plasma treatment is to increase themicro-roughness of the surface of the electric conductor, which also hasa positive effect on the adhesion of the insulating coating.

In order to prevent the reformation of an oxide layer on the surface ofthe electric conductor, at least part of the insulating coating isapplied to the surface of the electric conductor under a protective gasatmosphere, preferably under the same protective gas atmosphere underwhich the plasma treatment is carried out.

In order to achieve the object set out above, it is therefore providedaccording to the invention that the insulated electric conductorcomprises an electric conductor, preferably of copper or aluminum, withan insulating coating,

wherein the insulating coating either comprises

-   -   at least one insulating layer made of thermoplastic material,        or    -   at least one insulating layer made of thermoplastic material and    -   a plastic-containing intermediate layer, preferably a plasma        polymer layer or at least one fluoropolymer layer,        obtainable by a method in which the electric conductor is placed        under a protective gas atmosphere and is bombarded with ions of        s the protective gas in a gas plasma in order to remove an oxide        layer formed on a surface of the electric conductor and/or to        increase the surface energy of the electric conductor,        and subsequently either    -   the at least one insulating layer is applied directly to the        surface of the electric conductor under protective gas        atmosphere        or, in the case that the coating comprises the        plastic-containing intermediate layer,    -   at least the plastic-containing intermediate layer of the        insulating coating is applied directly under protective gas        atmosphere to the surface of the electric conductor.

An insulated electric conductor according to the invention hasparticularly good adhesion properties by the direct application of aplastic-containing intermediate layer of the insulating coating or bythe direct application of the insulating layer of thermoplastic materialon the plasma-treated and thus oxide-layer-free surface of the electricconductor: If a circular cut is performed around the insulated electricconductor perpendicular to a conductor axis and the conductor isstretched by 20%, the detachment of the insulating coating from theelectric conductor measured in the direction of the conductor axis isonly at most 3 mm, preferably at most 2 mm, in particular at most 1 mm.

The adhesion effect is thus achieved in both variants in that a plasticlayer, which preferably consists of plastic, is applied directly underprotective gas atmosphere on the plasma-cleaned and thus oxidelayer-free surface of the electric conductor. On the one hand, theplastic layer may directly be the at least one insulating layer made ofthermoplastic material if no intermediate layer is provided. On theother hand, the plastic layer can also be a plastic-containingintermediate layer, preferably a plasma polymer layer or at least onefluoropolymer layer. If the insulating coating has a plastic-containingintermediate layer, the at least one insulating layer is preferablyapplied directly to the plastic-containing intermediate layer. However,it is also conceivable that one or more further intermediate layers areprovided between the plastic-containing intermediate layer and the atleast one insulating layer.

Although a plurality of different plastics is conceivable which aresuitable as material for the plastic-containing intermediate layer ofthe insulating coating, the plastic-containing intermediate layer of theinsulating coating is preferably the plasma polymer layer or the atleast one fluoropolymer layer.

If no plastic-containing intermediate layer is provided and theinsulating layer is applied directly to the surface of the electricconductor, it is particularly preferred if the insulating coatingconsists of the at least one insulating layer, i.e. it has no furtherintermediate layers.

Surprisingly, it has been found in the context of test series that thedetachment of the insulating coating from the electric conductor usuallyremains far below 1 mm, in particular at most 0.2 mm, preferably at most0.1 mm, more preferably at most 0.05 mm, particularly preferably at most0.01 mm, when the at least one insulating layer is applied directly tothe surface of the electric conductor. Particularly advantageous effectscan be achieved in that the at least one insulating layer comprises apolyaryletherketone [PAEK], in particular polyetheretherketone (PEEK),or consists of polyaryletherketone [PAEK], in particularpolyetheretherketone [PEEK].

The same effects of the invention can be achieved in an insulatedelectric conductor comprising an electric conductor, preferably made ofcopper or aluminum, having an insulating coating,

wherein the insulating coating either comprises

-   -   at least one insulating layer made of thermoplastic material,        or    -   at least one insulating layer made of thermoplastic material and    -   a plastic-containing intermediate layer, preferably a plasma        polymer layer or at least one fluoropolymer layer,        in such a way that an oxide layer formed on a surface of the        electric conductor is removed, preferably by bombardment of the        electric conductor with ions of a protective gas of a protective        gas atmosphere in a gas plasma,        and subsequently either    -   the at least one insulating layer is applied directly to the        oxide-layer-free surface of the electric conductor        or, in the case that the coating comprises the        plastic-containing intermediate layer,    -   at least the plastic-containing intermediate layer of the        insulating coating is applied directly to the oxide-free surface        of the electric conductor.

An embodiment variant of the invention provides that the electricconductor is arranged continuously under a protective gas atmosphereuntil the application of the insulating coating in order to prevent theformation of a new oxide layer on the surface of the electric conductor.It is also possible to pass through several protective gas atmospheresin succession, as long as the plasma-treated electric conductor isarranged uninterruptedly under one of the inert gas atmospheres.

In a further embodiment variant of the invention, it is provided thatthe gas plasma for bombarding the electric conductor concerns alow-pressure plasma, preferably having a pressure below 80 mbar, whichcan be produced in a manner known per se. For example, pressures below50 mbar or even below 20 mbar are conceivable.

In order to enable the use of the insulated electric conductor in anenvironment with elevated temperature, for example in electricalmachines with increased operating temperature, it is provided in afurther embodiment variant of the invention that the insulating coating,in particular the at least one insulating layer, has a temperatureresistance of at least 180° C., preferably of at least 200° C., inparticular of at least 220° C.

Particularly good properties in terms of temperature resistance andresistance to a variety of organic and chemical solvents, in particularalso against hydrolysis, are achieved in a preferred embodiment of theinsulated electric conductor according to the invention and the methodaccording to the invention in that the thermoplastic material of the atleast one insulating layer is selected from the group consisting ofpolyaryletherketone [PAEK], polyimide [PI], polyamideimide [PAI],polyetherimide [PEI], polyphenylene sulfide [PPS], and combinationsthereof. It is understood that the thermoplastic material may compriseone or more of the above-mentioned plastics and optionally furtherconstituents, such as fiber material, fillers or other plastics.Polyaryletherketones are composed phenyl groups linked by means ofoxygen bridges, i.e. ether or ketone groups, wherein the number andsequence of ether or ketone groups within the polyaryletherketones isvariable. Polyimides are plastics whose most important structuralfeature is the imide group. These include polysuccinimide (PSI),polybismaleimide (PBMI) and polyoxadiazobenzimidazole (PBO), polyimidesulfone (PISO) and polymethacrylimide (PMI).

Accordingly, in a particularly preferred embodiment variant of theinsulated electric conductor according to the invention and the methodaccording to the invention, it is provided that the thermoplasticmaterial of the at least one insulating layer is a polyaryletherketone[PAEK] selected from the group consisting of polyetherketone [PEK],polyetheretherketone [PEEK], polyetherketoneketone [PEKK],polyetheretherketoneketone [PEEKK], polyetherketoneetherketoneketone[PEKEKK], and combinations thereof. Polyetheretherketone [PEEK] hasproven to be particularly suitable for the at least one insulatinglayer.

In a further embodiment variant of the invention, it is provided thatthe at least one insulating layer has a thickness between 10 and 1000μm, preferably between 25 μm and 750 μm, particularly preferably between30 μm and 500 μm, in particular between 50 μm and 250 μm. It isunderstood that other layer thicknesses are conceivable, for example 40μm, 60 μm, 80 μm, 100 μm or 200 μm, to name a few possibilities. It isunderstood that the stated values can relate both to the thickness of asingle layer of the insulating layer and also to the total thickness ofthe insulating layer if the insulating layer comprises more than onelayer.

The at least one insulating layer can be produced cheaply and quickly ifit is applied by an extrusion process, i.e. it is extrusion-coated.Therefore, in a further preferred embodiment variant of the invention,it is provided that the, preferably outer, insulating layer can beproduced by means of an extrusion method.

If the insulating coating consists of the at least one insulating layerand the at least one insulating layer is applied directly to the surfaceof the electric conductor, a particularly simple and cost-effectiveproduction of an insulated electric conductor according to the inventionis made possible because the adhesion of the at least one insulatinglayer to the surface of the electric conductor by the plasma treatmentis already so good that no intermediate layers are necessary.

Therefore, in a further particularly preferred embodiment variant of theinvention, it is provided that the insulating coating consists of the atleast one insulating layer and that the intermediate layer which isdirectly applied to the surface of the electric conductor and containsthe plastic is the at least one insulating layer.

Thus, the particularly preferred embodiment relates to an insulatedelectric conductor comprising an electric conductor, preferably made ofcopper or aluminum, having an insulating coating, wherein the insulatingcoating consists of at least one insulating layer of thermoplasticmaterial, obtainable by a method in which the electric conductor isplaced under a protective gas atmosphere and is bombarded with ions ofthe protective gas in a gas plasma to remove an oxide layer formed on asurface of the electric conductor and/or to increase the surface energyof the electric conductor, and the at least one insulating layer isapplied directly to the surface of the electric conductor, the at leastone insulating layer is applied to the electric conductor underprotective gas atmosphere.

In the same way, the particularly preferred embodiment also relates toan insulated electric conductor comprising an electric conductor,preferably made of copper or aluminum, having an insulating coating,wherein the insulating coating consists of at least one insulating layerof thermoplastic material, wherein according to the invention it isprovided that an oxide layer formed on a surface of the electricconductor is removed by bombardment of the electric conductor with ionsof a protective gas of a protective gas atmosphere in a gas plasma andsubsequently the at least one insulating layer is applied directly tothe oxide-layer-free surface of the electric conductor.

The insulating coating may, for example, only consist of a singleinsulating layer, which is applied directly to the surface of theelectric conductor in order to allow a particularly simple production.

However, in order to drastically reduce the likelihood of a defect inthe insulating coating, for example a section of the electric conductornot provided with the insulating coating due to an error in theproduction process of an insulating layer, it is provided in a furtherparticularly preferred embodiment of the invention that the insulatingcoating consists of exactly two or more than two, for example, three orfour, insulating layers. In this case, a lowermost insulating layer isapplied directly to the surface of the electric conductor, wherein thefurther insulating layers are respectively applied to one of thepreceding insulating layers. If a defect has occurred in the lowermostinsulating layer, i.e. if a section of the electric conductor is notcovered by the lowermost insulating layer, then the probability thatprecisely the defective section of the lowermost insulating layer willnot be covered by the subsequent insulating layers will be reducedfollowing an exponential function. The higher the number of insulatinglayers, the lower the probability that a portion of the electricconductor has no insulating coating. In order to achieve the improvedadhesion of the subsequent insulating layers to the electric conductor,all insulating layers are applied under a protective gas atmosphere, sothat the adhesion of subsequent insulating layers is ensured in theregion of defective sections of the preceding insulating layers.

In principle, at least one, for example one, two, three or four, furtherinsulating layer of thermoplastic material can be applied to theinsulating coating or to the insulating coating consisting of the atleast one insulating layer. The at least one further insulating layer ispreferably constructed analogously to the at least one insulating layer,so that the thermoplastic material of the at least one furtherinsulating layer is selected from the group consisting ofpolyaryletherketone [PAEK], in particular polyetheretherketone [PEEK],polyimide [PI], polyamideimide [PAI], Polyetherimide [PEI],polyphenylene sulfide [PPS], and combinations thereof.

Since the defective sections of the at least one insulating layer aregenerally relatively small areas, it is also conceivable for at leastone further insulating layer to be applied outside the protective gasatmosphere to the insulating coating in order to cover any defectivesections of the insulating coating in the region of the defectiveportions of the insulating coating, so that the adhesion of the furtherinsulating layer is not improved in the region of the defective portionsof the insulating coating. It is understood that other insulating layerscan be applied, if a greater thickness of the insulation is required.Therefore, in a further embodiment variant of the invention, it isprovided that at least one further insulating layer, preferably one, twoor three thereof, is applied to the insulating coating, wherein the atleast one further insulating layer is not applied under a protective gasatmosphere.

In a first alternative embodiment variant of the invention, in order toimprove the adhesion of the insulating coating to the surface of theelectric conductor, it is provided that the insulating coating has aplasma polymer layer of cross-linked macromolecules of non-uniform chainlength applied directly to the surface of the electric conductor, whichplasma polymer layer can be produced by polymerization of a gaseousmonomer in a gas plasma, preferably in the gas plasma for bombarding theelectric conductor. In other words, the intermediate layer of theinsulating coating which is applied directly to the surface of theelectric conductor and contains plastic is the plasma polymer layer inthis exemplary embodiment. The plasma polymer layer serves as anintermediate layer and, on the one hand, adheres excellently to thesurface of the electric conductor and, on the other hand, enablesincreased adhesion of the layer of the insulating coating, for examplethe at least one insulating layer, that is applied to the plasma polymerlayer.

A further embodiment variant of the first alternative embodimentprovides that the plasma polymer layer has a thickness of 1 μm or less.Thicknesses of up to one hundredth of a micrometer are conceivable asthe lower limit. Due to the small layer thickness, the plasma polymerlayer has an insignificant effect on the entire thickness of theinsulated electric conductor.

According to a further embodiment variant of the first alternativeembodiment variant, the monomer for producing the plasma polymer layeris ethylene, buthenol, acetone or tetrafluoromethane [CF₄]. The plasmapolymer layers formed by these monomers in the plasma are distinguishedby particularly good adhesion properties. In particular, if the plasmapolymer layer should have similar properties as polytetrafluoroethylene[PTFE] or perfluoroethylene propylene [FEP], CF₄ is suitable as amonomer.

In a second alternative embodiment, it is provided that the insulatingcoating has at least one fluoropolymer layer, applied directly to thesurface of the electric conductor, preferably comprisingpolytetrafluoroethylene [PTFE] or perfluoroethylene propylene [FEP]. Thefluoropolymer layer is also distinguished by excellent adhesionproperties, both on the electric conductor and on the layer applied tothe fluoropolymer layer, and serves as an intermediate layer of theinsulating coating. It is also conceivable that several fluoropolymerlayers, for example two, three or four, are applied one above the otherto the electric conductor. Particularly advantageous adhesion propertiesare achieved in that the thickness of the at least one fluoropolymerlayer is between 1 μm and 120 μm, preferably between 5 μm and 100 μm,particularly preferably between 10 μm and 80 μm, in particular between20 μm and 50 μm.

In order to achieve the above-described improved adhesion properties forlayers of the insulating coating applied to the plasma polymer layer orthe at least one fluoropolymer layer, in particular for the at least oneinsulating layer, on the electric conductor, so that the adhesion ofsubsequent layers in the region of defective sections of the precedinglayers applied to the electric conductor is increased, the entireinsulating coating is applied in a preferred embodiment of the inventionunder a protective gas atmosphere.

In order to reduce the number of different layers in the insulatingcoating and to keep the associated production costs low, it is providedin a further embodiment of the invention that the at least oneinsulating layer is applied directly to the plasma polymer layer or theat least one fluoropolymer layer. In other words, the insulating coatingconsists of at least two layers: the first lower layer applied directlyto the electric conductor according to the first or second alternativeembodiment variant and the second upper layer in the form of at leastone insulating layer of thermoplastic material. The outermost layer ofthe insulating coating can be formed either by the at least oneinsulating layer itself or by one or more further layers.

The invention further relates to a method for producing an insulatedelectric conductor, which has the following method steps:

-   -   bombarding an electric conductor placed under a protective gas,        preferably made of copper or aluminum, with ions of the        protective gas in a gas plasma, preferably a low-pressure        plasma, to remove an oxide layer formed on the surface of the        electric conductor and/or to increase the surface energy of the        electric conductor;    -   applying an insulating coating to the surface of the electric        conductor, wherein the insulating coating either comprises    -   at least one insulating layer made of thermoplastic material,        or    -   at least one insulating layer made of thermoplastic material and    -   a plastic-containing intermediate layer, preferably a plasma        polymer layer or at least one fluoropolymer layer,        wherein either    -   the at least one insulating layer is applied directly to    -   the surface of the electric conductor under protective gas        atmosphere        or, in the case that the coating comprises the        plastic-containing intermediate layer,    -   at least the plastic-containing intermediate layer of the        insulating coating is applied directly under protective gas        atmosphere to the surface of the electric conductor.

The electric conductor, preferably made of copper or aluminum, issubjected to the method in the form of a band or a wire. In this case,the electric conductor is treated either “in-line”, i.e. directly afterthe production of the electric conductor (such as by cold forming orextrusion), according to the method according to the invention, or theelectric conductor is provided in a wound-up form via a coil outlet. Asa rule, the electric conductor is subjected to a mechanical and/orchemical pre-cleaning before the plasma treatment. The plasma treatmentis carried out analogously to the previous embodiments, wherein theelectric conductor is continuously conveyed through the plasma treatmentunit performing the plasma treatment. By suitable choice of the processparameters, the thickness of the layer removed by the plasma treatmentfrom the electric conductor can be adjusted precisely. In addition, itis also possible to define the temperature for the soft annealing andthe associated recrystallization of the microstructure of the electricconductor.

After the plasma treatment, i.e. the removal of the oxide layer and anyimpurities from the surface of the electric conductor, wherein even thinlayers (less than 1 μm, preferably less than 0.1 μm) of the surface ofthe electric conductor itself can be removed by bombardment with ions inthe gas plasma or the activation of the surface of the electricconductor, the insulating coating is applied to the treated surface ofthe electric conductor. The insulating coating adheres particularly wellto the surface of the electric conductor due to the removal of the oxidelayer or by the activation of the surface by increasing the surfaceenergy of the electric conductor. In order to prevent the formation of anew oxide layer on the surface of the electric conductor, which wouldprevent or at least significantly weaken the effect according to theinvention, either the at least one insulating layer or at least theplastic-containing intermediate layer of the insulating coating, i.e. inparticular the plasma polymer layer or at least one fluoropolymer layer,is applied under protective gas atmosphere directly to the oxidelayer-free surface of the electric conductor. In particular, it isadvantageous if the electric conductor is arranged continuously under aprotective gas atmosphere until the application of the insulatingcoating. It goes without saying that, provided that two, three or moreinsulating layers of thermoplastic material are provided, at least thefirst of the insulating layers is applied directly to the surface of theelectric conductor and the subsequent insulating layers are at leastpartially applied to the underlying insulating layers.

Insulated electric conductors produced in this manner show particularlygood adhesion properties as a result of the direct application of aplastic-containing intermediate layer of the insulating coating or bythe direct application of at least one insulating layer of thermoplasticmaterial on the plasma-treated, oxide-free surface of the electricconductor: If a circular cut is carried out perpendicular to a conductoraxis on the insulated electric conductor and the conductor is stretchedby 20%, the detachment of the insulating coating from the electricconductor measured in the direction of the conductor axis is only atmost 3 mm, preferably at most 2 mm, in particular at most 1 mm.

If the at least one insulating layer of thermoplastic material isapplied directly to the surface of the electric conductor, it has beenfound that the detachment of the insulating coating from the electricconductor usually remains far below 1 mm, in particular not more than0.2 mm, preferably not more than 0.1 mm, more preferably not more than0.05 mm, particularly preferably not more than 0.01 mm. Particularlyadvantageous effects are achieved when the thermoplastic material of theat least one insulating layer is selected from the group consisting ofpolyaryletherketone [PAEK], in particular polyetheretherketone [PEEK],polyimide [PI], polyamideimide [PAI], polyetherimide [PEI],polyphenylene sulfide [PPS] and combinations thereof.

A variant of the method provides that the at least one insulating layeris extrusion-coated. Extrusion is a cost-effective method for applyingthe insulating layer and is particularly also suitable for PAEK, inparticular PEEK, and PPS. The at least one insulating layer can thusalso be applied in a simple manner as the outermost layer of theinsulating coating.

By preheating the electric conductor, which is particularly advantageouswhen the at least one insulating layer or the insulating coating isextruded directly onto the surface of the electric conductor, a suddencooling of the plastic-containing intermediate layer is reduced incontact with the electric conductor and thus negative influences on theadhesion minimized. Likewise, it can be provided that the electricconductor is cooled before applying the insulating coating in order toprevent excessive heating, such as a melt, of the plastic-containingintermediate layer in contact with the electric conductor. Therefore, itis provided in a further preferred embodiment variant of the methodaccording to the invention that the electric conductor is brought to atemperature of at least 200° C., preferably at least 400° C., prior tothe application of the insulating coating.

In a further embodiment variant of the invention, it is provided thatafter the at least one insulating layer has been extrusion-coated, theinsulated electric conductor is cooled depending on the strength of theat least one insulating layer to be achieved. The adjustment of themechanical properties of the at least one insulating layer, inparticular the mechanical strength, takes place, inter alia, by thedefined cooling of the insulated electric conductor and the consequentadjustment of the degree of crystallization, and is particularlyimportant if the at least one insulating layer is the outermost layerthe insulating coating. If, for example, the insulated electricconductor is cooled slowly, for example by cooling in the air, a highdegree of crystallinity of the at least one insulating layer isachieved. It is also conceivable to provide quenching in a water bath,therefore an abrupt cooling, or a combination of abrupt and slowcooling.

In order to further improve the adhesion of the insulating coating tothe electric conductor, in particular if the at least one insulatinglayer is applied directly to the surface of the electric conductor, itis provided in a preferred embodiment of the method according to theinvention that the insulated electric conductor, after extruding the atleast one insulating layer onto the surface, is guided via rollers,preferably pressure rollers. It is particularly advantageous in thiscase if the at least one insulating layer forms the outermost layer ofthe insulating coating. Tight guiding of the insulated electricconductor via the pressure rollers under pressure of the insulatedelectric conductor leads to a particularly good adhesion of theinsulating coating or in particular of the at least one insulating layeron the surface of the electric conductor. In this case, the boundarysurfaces of the insulating coating between the individual layers, ifseveral are present, and/or the boundary surfaces of the lowermost layerof the insulating coating and the surface of the electric conductor arepressed together, thus enhancing the adhesion effects.

In a particularly preferred embodiment variant of the invention, whichis characterized by particularly good adhesion properties, it isprovided that the insulating coating consists of at least one insulatinglayer and that the at least one insulating layer is applied directly tothe surface of the electrical conductor as a plastic-containingintermediate layer of the insulating coating under a protective gasatmosphere. Accordingly, the following method step is carried out:

Applying an insulating coating to the surface of the electric conductor,wherein the insulating coating consists of at least one insulating layerof thermoplastic material and wherein the at least one insulating layeris applied under protective gas atmosphere directly to the surface ofthe electric conductor.

This also achieves the previously mentioned particularly low detachmentof less than 1 mm.

In order, as mentioned above, to drastically reduce the probability of adefect in the insulating coating, it is provided in another embodimentvariant that the insulating coating consists of at least two, preferablyexactly two, insulating layers and the insulating coating is produced bytandem extrusion under a protective gas atmosphere. Due to the tandemextrusion, the at least two insulating layers are produced independentlyof one another, so that an obstruction of an extrusion tool only causesa defect in one of the insulating layers. As a result, the defectivesection is covered by the subsequent extrusion steps with highprobability.

If, as stated above, due to the relatively small area of the defects,improved adhesion can be dispensed with or a thicker insulating coatingis required, a further embodiment variant of the invention provides thatat least one further insulating layer of thermoplastic material isextruded by tandem extrusion onto the insulating coating, wherein theextrusion of the further insulating layer does not take place under aprotective gas atmosphere.

Preferably, the thermoplastic material of the at least one furtherinsulating layer is selected from the group consisting ofpolyaryletherketone [PAEK], in particular polyetheretherketone [PEEK],polyimide [PI], polyamideimide [PAI], polyetherimide [PEI],polyphenylene sulfide [PPS] and combinations thereof.

If the insulating coating comprises at least one fluoropolymer layer,which is applied as a plastic-containing intermediate layer directly tothe surface of the electric conductor, the steps required for theproduction of the insulating coating can be reduced by the fact that theat least one insulating layer and the at least one fluoropolymer layercan be prepared by co-extrusion or tandem extrusion. Thus, both layerscan be produced in a single manufacturing step and with an extrusionunit.

In order to improve the adhesion of the insulating coating to theelectric conductor, it is provided in a further embodiment that a plasmapolymer layer is applied directly to the surface of the electricconductor by polymerization of a gaseous monomer in a gas plasma as aplastic-containing intermediate layer.

Since high temperature resistance and high adhesion of the insulatingcoating on the electric conductor is important, in particular inelectrical engineering, it is provided according to the invention thatan insulated electric conductor according to the invention is used as awinding wire for electrical machines, preferably electric motors ortransformers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail below with referenceto exemplary embodiments. The drawings are provided by way of exampleand are intended to explain the concept of the invention, but shall inno way restrict it or even render it conclusively, wherein:

FIG. 1 shows a schematic representation of a method according to theinvention;

FIG. 2a shows a first embodiment variant of an insulated electricconductor with a rectangular cross-section;

FIG. 2b shows a second embodiment variant of an insulated electricconductor with a rectangular cross-section.

FIG. 2c shows a third embodiment variant of an insulated electricconductor with a rectangular cross-section;

FIGS. 3a-3c show the first to third embodiment variant with a roundcross-section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic representation of a method for producing aninsulated electric conductor, as shown in FIGS. 2a to 2d and 3a to 3d .The insulated electric conductor comprises an electric conductor 1 madeof copper, wherein other materials such as aluminum are conceivable, andan insulating coating 2, which has at least one insulating layer 3 madeof thermoplastic material (also called thermoplastic resin,thermoplastic synthetic material or thermoplastic polymer), preferably ahigh-temperature-resistant plastic. In the following exemplaryembodiments, the at least one insulating layer 3 is formed as an outerinsulating layer 3 and thus forms the outermost layer of the insulatingcoating 2. It is understood, however, that in alternative embodimentvariants still one or more further layers, preferably insulating layers,may be applied to the insulating layer 3, which can then form theoutermost layer of the insulating coating 2.

The electric conductor 1 is continuously supplied in the illustratedembodiment as a band or wire via a coil outlet 7 to the process and canbe prepared for example by means of cold forming processes, such asdrawing or rolling, or extrusion, for example by means of Conform®technology. It goes without saying that the method according to theinvention can also be carried out “in-line”, i.e. directly connected tothe production process. In a first step, the electric conductor 1 ispre-cleaned mechanically in a pre-cleaning unit 8, for example by meansof a grinding process, or chemically, for example by means of suitablesolvents or acids, in order to remove coarse soiling from the electricconductor 1.

In the next method step, the pre-cleaned electric conductor 1 enters aplasma treatment unit 9 in which a protective gas atmosphere ofnitrogen, argon or hydrogen is present and a gas plasma in the form of alow-pressure plasma is produced with less than 20 mbar pressure.However, a low-pressure plasma can already be produced even at apressure of less than 80 mbar. In this low-pressure plasma, the surfaceof the electric conductor 1 is bombarded with ions of the protective gasin order to carry off or remove an oxide layer formed on a surface ofthe electric conductor 1. At the same time, the electric conductor 1 issoft-annealed by the plasma treatment and the surface energy of theelectric conductor 1 therefore increases, thus activating the surface.

By removing the oxide layer and any contaminants from the surface of theelectric conductor 1, wherein it may even be provided that very thinlayers of the electric conductor 1 itself are removed from the surface,and by the increase of the surface energy, the adhesion between theelectric conductor 1 made of copper and the insulating coating 2 appliedto the electric conductor 1 can be improved decisively.

In the first embodiment variant of the insulated electric conductoraccording to the invention, shown in FIG. 2a as a flat conductor with arectangular cross-section and, in FIG. 3a with a round cross-section,the insulating coating 2 consists only of an insulating layer 3. Theinsulating layer 3 has a temperature resistance of more than 180° C.,preferably above 220° C., so that the insulated electric conductor canbe used even at high operating temperatures. The outer insulating layer3 consists of polyetheretherketone [PEEK], which has both hightemperature resistance and high resistance to a large number of organicand inorganic substances. Alternatively, the outer insulating layer 3may also consist of polyphenylene sulfide [PPS] or comprise PEEK and/orPPS.

In order to achieve the increased adhesion between the electricconductor 1 and the outer insulating layer 3, the electric conductor 1reaches the extrusion unit 11 after passing through the plasma treatmentunit 9, in which the outer insulating layer 3 is extrusion-coated ontothe electric conductor 1. In this case, the electric conductor 1 ispreheated to a temperature of at least 200° C., preferably at least 300°C. In order to prevent the re-formation of an oxide layer, both theextrusion and the transport of the conductor 1 into the extrusion unit11 takes place under a protective gas atmosphere. An insulated electricconductor produced in this way can be used, for example, as a windingwire, which is also known in English as a “magnet wire”, in an electricmachine, such as an electric motor or a transformer. The thickness ofthe outer insulating layer 3 is about 30 μm in the present exemplaryembodiment.

In particular, when the insulating layer 3 consists of apolyaryletherketone [PAEK], such as polyetheretherketone [PEEK],particularly good adhesion properties are achieved. Thus, the detachmentof the insulating layer 3 from the electric conductor 1 usually remainswell below 1 mm, and is in particular at most 0.2 mm, preferably at most0.1 mm, more preferably at most 0.05 mm, particularly preferably at most0.01 mm. Even if the thermoplastic material of the insulating layer 3 ispolyimide [PI], polyamideimide [PAI], polyetherimide [PEI],polyphenylene sulfide [PPS], increased adhesion properties can beachieved.

In general, the at least one insulating layer 3 may also comprise two,three, four or more individual insulating layers 3, all of which areproduced under a protective gas atmosphere in the extrusion unit 11. Asa result, the probability of defects in the insulating coating 2 can bedrastically reduced, since defects in the lowermost of the insulatinglayers 3 are compensated by subsequent insulating layers 3. Tandemextrusion processes are particularly suitable for such a preparation.

Additionally or instead, it may also be provided that further insulatinglayers, which are preferably constructed analogously to the at least oneinsulating layer 3, i.e. in particular of a polyaryletherketone [PAEK]such as polyetheretherketone [PEEK] or another of the aforementionedplastics, are applied to the insulating coating 2 outside the protectivegas atmosphere in a further extrusion unit 12.

In order to increase the adhesion between the insulating coating 2 andthe electric conductor 1 as an alternative to the first embodimentvariant, the insulating coating 2 comprises in the second embodimentshown in FIGS. 2b and 3b , in addition to the outer insulating layer 3made of PEEK or PPS, a plastic-containing intermediate layer in form ofa plasma polymer layer 4. This plasma polymer layer 4 is produced in themethod according to the invention in a plasma polymerization unit 10,which is arranged after the plasma treatment unit 9 and before theextrusion unit 11. It is also conceivable that the plasma treatment andthe plasma polymerization are carried out in a combined device. In theplasma polymerization unit 10, after the oxide layer is removed andsurface energy increased, as above, the plasma polymer layer 4 is formedon the surface of the electric conductor 1 by activating a gaseousmonomer such as ethylene, butenol, acetone or tetrafluoromethane [CF₄]by the plasma and thereby forming highly cross-linked macromolecules ofdifferent chain length and a proportion of free radicals, which depositas a plasma polymer layer 4 on the surface of the electric conductor 1.In the present exemplary embodiment, the resulting plasma polymer layer4 is less than 1 μm thick and adheres particularly well to the activatedand oxide-free surface of the electric conductor 1.

The outer insulating layer 3 is in turn extruded in the extrusion unit11 onto the plasma polymer layer 4 as described above, wherein theadhesion between the plasma polymer layer 4 and the outer insulatinglayer 3 is also high.

In the third embodiment variant, illustrated in FIGS. 2c and 3c , theinsulating coating 2 comprises, in addition to the outer insulatinglayer 3 made of PEEK, a plastic-containing intermediate layer formed asa fluoropolymer layer 5 of polytetrafluoroethylene [PTFE] orperfluoroethylene propylene [FEP], which is applied directly to thesurface of the electric conductor 1 and further improves the adhesionbetween the electric conductor 1 and the outer insulating layer 3. Thefluoropolymer layer 5 is produced together with the outer insulatinglayer 3 in the extrusion unit 11 by means of a co-extrusion or tandemextrusion process. The thickness of the fluoropolymer layer 5 is about30 μm in the present embodiment.

After extrusion-coating the outer insulating layer 3, the insulatedelectric conductor is cooled in a controlled manner, for example by aircooling, and passed over a series of pressure rollers which furtherimprove adhesion by applying pressure to the insulated electricconductor. Finally, the insulated electric conductor is wound on a coilwinder 13.

The illustrated devices in FIG. 1 concern an overview in which alldevices are shown, which are necessary for the production of theindividual embodiment variants. While the sequence, from right to left,of the devices passed through are independent of the embodiment variantand in any case the plasma treatment unit 9 and the extrusion unit 11have to be passed, the plasma polymerization unit 9 and the furtherextrusion unit 12 are optional devices which are used only in theproduction of specific design variants. It is understood that instead ofa co-extrusion or tandem extrusion process, several individualextrusions can be carried out sequentially.

LIST OF REFERENCE NUMERALS

-   -   1 Electric conductor    -   2 Insulating coating    -   3 Insulating layer    -   4 Plasma polymer layer    -   Fluoropolymer layer    -   6 Metal layer    -   7 Coil outlet    -   8 Precleaning unit    -   9 Plasma treatment unit    -   10 Plasma polymerization unit    -   11 Extrusion unit    -   12 Further extrusion unit    -   13 Coil winder

1. An insulated electric conductor, comprising an electric conductorhaving an insulating coating, wherein the insulating coating eithercomprises at least one insulating layer made of thermoplastic material,or at least one insulating layer made of thermoplastic material and aplastic-containing intermediate layer, obtainable by a method in whichthe electric conductor is placed under a protective gas atmosphere andis bombarded with ions of the protective gas in a gas plasma in order toremove an oxide layer formed on a surface of the electric conductorand/or to increase the surface energy of the electric conductor, andsubsequently either the at least one insulating layer is applieddirectly to the surface of the electric conductor under protective gasatmosphere or, in case the coating comprises the plastic-containingintermediate layer, at least the plastic-containing intermediate layeris applied directly under protective gas atmosphere to the surface ofthe electric conductor.
 2. The insulated electric conductor according toclaim 1, wherein the electric conductor is placed continuously underprotective gas atmosphere until the application of the insulatingcoating in order to prevent the formation of a new oxide layer on thesurface of the electric conductor.
 3. The insulated electric conductoraccording to claim 1, wherein the gas plasma for bombarding the electricconductor is a low-pressure plasma.
 4. The insulated electric conductoraccording to claim 1, wherein the insulating coating has a temperatureresistance of at least 180° C.
 5. The insulated electric conductoraccording to claim 1, wherein the thermoplastic material of the at leastone insulating layer is selected from the group consisting ofpolyaryletherketone [PAEK], polyimide [PI], polyamideimide [PAI],polyetherimide [PEI], polyphenylene sulfide [PPS] and combinationsthereof.
 6. The insulated electric conductor according to claim 1,wherein the thermoplastic material of the at least one insulating layeris a polyaryletherketone [PAEK] selected from the group consisting ofpolyetherketone [PEK], polyetheretherketone [PEEK],polyetherketoneketone [PEKK], polyetheretherketoneketone [PEEKK],polyetherketoneetherketoneketone [PEKEKK] and combinations thereof. 7.The insulated electric conductor according to claim 1, wherein the atleast one insulating layer has a thickness between 10 and 1000 μm. 8.The insulated electric conductor according to claim 1, wherein the atleast one insulating layer can be produced by means of an extrusionmethod.
 9. The insulated electric conductor according to claim 1,wherein the insulating coating consists of the at least one insulatinglayer.
 10. The insulated electric conductor according to claim 9,wherein the insulating coating consists of one insulating layer or twoinsulating layers or at least two insulating layers.
 11. (canceled) 12.The insulated electric conductor according to claim 1, wherein at leastone further insulating layer made of thermoplastic material is appliedto the insulating coating, wherein the at least one further insulatinglayer is not applied under a protective gas atmosphere.
 13. Theinsulated electric conductor according to claim 12, wherein thethermoplastic material of the at least one further insulating layer isselected from the group consisting of polyaryletherketone [PAEK],polyetheretherketone [PEEK], polyimide [PI], polyamideimide [PAI],polyetherimide [PEI], polyphenylene sulfide [PPS] and combinationsthereof.
 14. (canceled)
 15. (canceled)
 16. (canceled)
 17. The insulatedelectric conductor according to claim 1, wherein the insulating coatinghas at least one fluoropolymer layer, and the plastic-containingintermediate layer which is applied directly to the surface of theelectric conductor consists of the fluoropolymer layer.
 18. Theinsulated electric conductor according to claim 17, wherein thefluoropolymer layer comprises polytetrafluoroethylene [PTFE] orperfluoroethylene propylene [FEP].
 19. The insulated electric conductoraccording to claim 17, wherein the thickness of the at least onefluoropolymer layer is between 1 μm and 120 μm.
 20. The insulatedelectric conductor according to claim 17, wherein the entire insulatingcoating is applied to the electric conductor under-protective gasatmosphere.
 21. An insulated electric conductor, comprising an electricconductor having an insulating coating, wherein the insulating coatingeither comprises at least one insulating layer made of thermoplasticmaterial, or at least one insulating layer made of thermoplasticmaterial and a plastic-containing intermediate layer, further comprisingthat an oxide layer formed on a surface of the electric conductor isremoved by bombardment of the electric conductor with ions of aprotective gas of a protective gas atmosphere in a gas plasma, andsubsequently either the at least one insulating layer is applieddirectly to the oxide-layer-free surface of the electric conductor or,in case the coating comprises the plastic-containing intermediate layer,at least the plastic-containing intermediate layer is applied directlyto the oxide-layer-free surface of the electric conductor. 22.(canceled)
 23. The insulated electric conductor according to claim 21,wherein the thermoplastic material of the at least one insulating layeris selected from the group consisting of polyaryletherketone [PAEK],polyimide [PI], polyamideimide [PAI], polyetherimide [PEI],polyphenylene sulfide [PPS] and combinations thereof.
 24. The insulatedelectric conductor according to claim 21, wherein the thermoplasticmaterial of the at least one insulating layer is a polyaryletherketone[PAEK] selected from the group consisting of polyetherketone [PEK],polyetheretherketone [PEEK], polyetherketoneketone [PEKK],polyetheretherketoneketone [PEEKK], polyetherketoneetherketoneketone[PEKEKK], and combinations thereof.
 25. (canceled)
 26. (canceled) 27.The insulated electric conductor according to claim 21, wherein theinsulating coating consists of the at least one insulating layer. 28.The insulated electric conductor according to claim 27, wherein theinsulating coating consists of one insulating layer or two insulatinglayers or at least two insulating layers.
 29. (canceled)
 30. Theinsulated electric conductor according to claim 21, wherein at least onefurther insulating layer of thermoplastic material is applied to theinsulating coating, wherein the at least one further insulating layer isnot applied under protective gas atmosphere.
 31. The insulated electricconductor according to claim 30, wherein the thermoplastic material ofthe at least one further insulating layer is selected from the groupconsisting of polyaryletherketone [PAEK], polyetheretherketone [PEEK],polyimide [PI], polyamideimide [PAI], polyetherimide [PEI],polyphenylene sulfide [PPS] and combinations thereof.
 32. (canceled) 33.(canceled)
 34. (canceled)
 35. (canceled)
 36. (canceled)
 37. (canceled)38. (canceled)
 39. A method for producing an insulated electricconductor, which comprises the following method steps: bombarding anelectric conductor which is arranged under a protective gas, with ionsof the protective gas in a gas plasma in order to remove an oxide layerformed on the surface of the electric conductor and/or to increase thesurface energy of the electric conductor; applying an insulating coatingto the surface of the electric conductor, wherein the insulating coatingcomprises either at least one insulating layer made of thermoplasticmaterial, or at least one insulating layer made of thermoplasticmaterial and a plastic-containing intermediate layer, wherein either theat least one insulating layer is applied directly to the surface of theelectric conductor under protective gas atmosphere or, in case thecoating comprises the plastic-containing intermediate layer, at leastthe plastic-containing intermediate layer is applied directly underprotective gas atmosphere to the surface of the electric conductor. 40.The method according to claim 39, wherein the thermoplastic material ofthe at least one insulating layer is selected from the group consistingof polyaryletherketone [PAEK], polyimide [PI], polyamideimide [PAI],polyetherimide [PEI], polyphenylene sulfide [PPS] and combinationsthereof.
 41. The method according to claim 39, wherein the thermoplasticmaterial of the at least one insulating layer (3) is apolyaryletherketone [PAEK] selected from the group consisting ofpolyetherketone [PEK], polyetheretherketone [PEEK],polyetherketoneketone [PEKK], polyetheretherketoneketone [PEEKK],polyetherketoneetherketoneketone [PEKEKK] and combinations thereof. 42.The method according to claim 39, wherein the at least one insulatinglayer is extrusion-coated.
 43. The method according to claim 39, whereinthe electric conductor is brought to a temperature of at least 200° C.before the application of the insulating coating.
 44. The methodaccording to claim 42, wherein the insulated electric conductor iscooled after the extrusion-coating of the at least one insulating layerdepending on the achievable strength of the at least one insulatinglayer.
 45. The method according to claim 42, wherein the insulatedelectric conductor is guided via rollers after the extrusion-coating ofthe at least one insulating layer.
 46. The method according to claim 42,wherein the insulating coating consists of the at least one insulatinglayer.
 47. The method according to claim 46, wherein the insulatingcoating consists of at least two insulating layers and the insulatingcoating is produced by tandem extrusion under a protective gasatmosphere.
 48. The method according to one claim 46, wherein at leastone further insulating layer of thermoplastic material isextrusion-coated onto the insulating coating by means of tandemextrusion, wherein the extrusion of the at least one further insulatinglayer does not take place under protective gas atmosphere.
 49. Themethod according to claim 48, wherein the thermoplastic material of theat least one further insulating layer is selected from the groupconsisting of polyaryletherketone [PAEK], in particularpolyetheretherketone [PEEK], polyimide [PI], polyamideimide [PAI],polyetherimide [PEI], polyphenylene sulfide [PPS] and combinationsthereof.
 50. (canceled)
 51. The method according to claim 42, whereinthe insulating coating comprises at least one at least one fluoropolymerlayer and the fluoropolymer layer is applied as a plastic-containingintermediate layer of the insulating coating under protective gasatmosphere directly to the surface of the electric conductor.
 52. Themethod according to claim 51, wherein at least one fluoropolymer layerand the at least one insulating layer are produced by co-extrusion ortandem extrusion.
 53. (canceled)
 54. The insulated electric conductoraccording to claim 5, wherein the at least one insulating layer has athickness between 10 and 1000 μm.
 55. The insulated electric conductoraccording to claim 6, wherein the at least one insulating layer has athickness between 10 and 1000 μm.
 56. The insulated electric conductoraccording to claim 5, wherein the at least one insulating layer can beproduced by means of an extrusion method.
 57. The insulated electricconductor according to claim 6, wherein the at least one insulatinglayer can be produced by means of an extrusion method.
 58. The insulatedelectric conductor according to claim 5, wherein the insulating coatingconsists of the at least one insulating layer.
 59. The insulatedelectric conductor according to claim 6, wherein the insulating coatingconsists of the at least one insulating layer.
 60. The insulatedelectric conductor according to claim 23, wherein the insulating coatingconsists of the at least one insulating layer.
 61. The insulatedelectric conductor according to claim 24, wherein the insulating coatingconsists of the at least one insulating layer.
 62. The method accordingto claim 40, wherein the at least one insulating layer isextrusion-coated.
 63. The method according to claim 41, wherein the atleast one insulating layer is extrusion-coated.
 64. The method accordingto claim 40, wherein the electric conductor is brought to a temperatureof at least 200° C. before the application of the insulating coating.65. The method according to claim 41, wherein the electric conductor isbrought to a temperature of at least 200° C. before the application ofthe insulating coating.
 66. The insulated electric conductor accordingto claim 1 wherein the electric conductor is made of aluminum or copper.67. The insulated electric conductor according to claim 5 wherein theelectric conductor is made of aluminum or copper.
 68. The insulatedelectric conductor according to claim 6 wherein the electric conductoris made of aluminum or copper.
 69. The insulated electric conductoraccording to claim 21 wherein the electric conductor is made of aluminumor copper.
 70. The insulated electric conductor according to claim 23wherein the electric conductor is made of aluminum or copper.
 71. Theinsulated electric conductor according to claim 24 wherein the electricconductor is made of aluminum or copper.
 72. The method according toclaim 39 wherein the electric conductor is made of aluminum or copper.73. The method according to claim 40 wherein the electric conductor ismade of aluminum or copper.
 74. The method according to claim 41 whereinthe electric conductor is made of aluminum or copper.